We will attempt to establish the etiology and pathogenesis of multiple sclerosis (MS) using several interdepartmental approaches. We will attempt to recover virus from MS patients in various stages of disease, search for morphologic evidence of the presence of virus, and utilize immunologic methods to look for evidence of continued infection of MS patients. We will characterize in a serial prospective fashion parameters of humoral and cell-mediated altered immune responsiveness, in correlation with the clinical course of a closely studies group of MS patients. These investigations may yield a more specific laboratory diagnostic test for multiple sclerosis. Techniques will include the methodology of virology, molecular biology, immunology, CNS organ culture, low and high voltage transmission and scanning electron microscopy, autoradiography and neurochemistry in conjunction with detailed neurologic characterization of patients participating in studies.